16 THE BOOK OF NATURE STUDY 



easy to draw a slide over the lips dislodging some of the flat 

 epithelial cells, and to compare these with a strip of transparent 

 skin peeled off a tulip leaf. 



(c) Resemblance in Development. When we trace the beech 

 tree back to the beginning of its life we find that the sapling 

 grew from a seedling, which came from an embryo within the 

 seed, and that this embryo arose from a unit element or egg-cell 

 fertilised by intimate union with another element derived from 

 the pollen grain. When we trace the squirrel back to the begin- 

 ning of its life we find that it also arises from a unit element or 

 egg-cell, borne by the female parent, which is fertilised by intimate 

 union with a male cell or spermatozoon produced by the male 

 parent. Indeed, all many-celled plants and animals begin as 

 fertilised egg-cells, except in cases of virgin birth (parthenogenesis), 

 or of asexual reproduction. From the egg-cell, which divides and 

 redivides after fertilisation, the body of the plant or animal is built 

 up of continued division, arrangement, and modification of cells. 



Summary. Plants and animals resemble one another in their 

 essential functions, in their cellular structure, and in their manner 

 of development. 



Contrasts. While there is no absolute distinction between 

 plants and animals, they represent divergent branches of a V- 

 shaped genealogical tree. It is easy to distinguish extremes 

 like bird and daisy, less easy to contrast sponge and mushroom, 

 and well-nigh impossible to decide whether some very simple 

 forms have a bias towards plants or towards animals. We cannot 

 do more than state average distinctions. 



As it is unnatural to the child's mind to care much about the 

 difficulty of finding absolute distinctions between two kinds of 

 creatures which seem as different as possible, we propose to 

 condense the time-honoured discussion into a table (page 15). 



SECTION 6. INTER-RELATIONS. Much more important from 

 the nature study outlook than " the distinctions between plants 

 and animals " are their inter-relations, (a) Plants are able to 

 feed on air, water, and salts, but animals have no such power 

 of living on the inorganic ; it follows, therefore, that in the long 

 run animal life depends on plant life for its continuance. (5) The 



